FIELD OF THE INVENTION
This invention relates to production equipment for oil wells and more particularly, to sucker rod guides for mounting in spaced relationship on the sucker rod string of a pumping well. The sucker rod guides of this invention may be color-coded for size identification and are each characterized by a generally cylindrically-shaped, smooth guide body having tapered top and bottom portions and a longitudinal, grooved bore which is preferably slightly undersized with respect to the sucker rod to which the sucker rod guides are attached. A tapered, inwardly expanding, longitudinal body slot extends longitudinally through the entire guide body of the sucker rod guide and communicates with the longitudinal bore, in order to provide a means for mounting one or more sucker rod guides on a sucker rod at a specific location or locations. In a preferred embodiment, the sucker rod guide of this invention is constructed by extruding a molten, self-lubricating plastic such as polyethylene, having an ultra-high molecular weight and density through a die to define a slotted cylinder having a smooth bore and a tapered longitudinal slot. Grooves may then be added to the bore by using a reaming tool to facilitate a more firm attachment to the sucker rod. Alternatively, the extruded, slotted cylinder can be centrally drilled to provide the longitudinal bore and the spaced grooves.
It has surprisingly been found that extruded molten polyethylene having an ultra-high molecular weight and corresponding ultra-high density produces a sucker rod guide that yields highly favorable abrasion and lubricating qualities, as well as a high tensile strength and a relatively high coefficient of thermal expansion, and other physical properties which are far superior to that of conventional sucker rod guides. In fact, it has been found by analysis and testing that extruded polyethylene plastic bar stock having a molecular weight in the range of approximately two million to six million, accounts for the superior physical characteristics of the extruded polyethylene. It has also been found that the polyethylene sucker rod guides of this invention are not adversely affected by hydrogen sulfide, salt water and other corrosive fluids and compounds normally found in an oil well.
Sucker rod guides of various description and composition are designed to fit on sucker rods used to pump oil wells, in order to eliminate, or at least greatly reduce, many of the down-hole problems which are characteristic of production equipment in oil wells. Because the ultra-high molecular weight, ultra-high density plastic sucker rod guides of this invention are generally characterized by a wet coefficient of friction which is lower than that of metal, they operate to increase the overall pumping efficiency of the wells, while at the same time prevent undesirable metal-to-metal contact between the reciprocating or spinning rods and the stationary tubing. Wear on sucker rod couplings used to make up the down-hole sucker rod string is also minimized, thus reducing the required inventory of costly rod parts. Tubing wear, often unseen until failure occurs, is also reduced, because the sucker rod guides receive the wear rather than the expensive tubing. The sucker rod guides of this invention also function as bearings to centralize the sucker rods in the tubing and even when the tubing buckles in a well during downstroke of the pumping unit, the sucker rods cannot contact the tubing due to the spaced positioning of the sucker rod guides on the sucker rods. Polish rod loads are also reduced because of the lower friction and less abrupt "stress reverse" which is realized when using the highly efficient sucker rod guides detailed herein. Accordingly, a properly designed sucker rod installation using the ultra-high molecular weight and, ultra-high density polyethylene sucker rod guides of this invention can realize significant savings in both equipment replacement and service costs in a pumping oil well. Fewer "pulling jobs", greater pumping efficiency and wells that stay in the pumping mode for longer periods of time, are proven results obtained from the use of the specially designed sucker rod guides of this invention.
Sucker rod guides of various design, size and materials of construction are well known in the art. Among the typical materials of construction are neoprene rubber and nylon and these materials are commonly used with metal inserts which encase and line the sucker rod guide bore, in order to facilitate better gripping of the sucker rod by the sucker rod guide and maintaining the sucker rod guide in a selected position on the sucker rod. However, it has been found that friction generated between the neoprene rubber sucker rod guides and the tubing as the sucker rod guide reciprocates or spins with the sucker rod string inside the tubing sometimes generates heat, which may result in a rapid deterioration of the neoprene material, thereby necessitating frequent "pulling jobs" in order to replace the guides. Furthermore, it has been found that nylon sucker rod guides are brittle and sometimes difficult to mount on a sucker rod without breaking, especially in cold weather. Sucker rod guides are typically secured to the respective lengths of sucker rod in spaced relationship, in order to space the sucker rod string from the tubing and protect both the sucker rod, sucker rod couplings and the tubing from excessive wear during the pumping operation. Since the reciprocating travel of each reciprocating sucker rod and sucker rod guide may be from approximately 3 feet to about 20 feet or more and this travel occurs at a rate of about 15 strokes per minute on the average, the material used to shape the sucker rod guide should be self-lubricating or easily lubricated by the well fluid and must have superior wear characteristics, in order to minimize the frequency of maintenance. Each sucker rod guide should also remain in the installed position on the sucker rod since the spacing of the guides prevents the sucker rod from contacting and damaging the tubing.
Accordingly, it is an object of this invention to provide a new and improved extruded plastic sucker rod guide having an ultra-high molecular weight, for mounting on the sucker rod of an oil well and preventing, or at least minimizing, metal-to-metal contact between the sucker rod and the tubing.
Another object of this invention is to provide a new and improved, injection-molded or compression molded, ultra-high density polyethylene sucker rod guide which is characterized by an exceptionally high abrasive resistance and good self-lubricating characteristics and is designed to tightly seat on the sucker rod of a pumping well at a specific location, with little or no displacement from the point of installation, to space the sucker rod from the tubing.
Still another object of the invention is to provide a sucker rod guide which is constructed of extruded polyethylene having an ultra-high molecular weight of at least 2 million for mounting on the sucker rod of a pumping unit in an oil well, which sucker rod guide includes a generally cylindrically-shaped body having a longitudinal, smooth or grooved sucker rod bore that is slightly undersized with respect to the sucker rod to which it is attached and further including an inwardly-expanding, tapered body slot extending longitudinally through the sucker rod guide body and communicating with the sucker rod bore, to facilitate mounting the sucker rod guide on the sucker rod.
Yet another object of the invention is to provide an extruded, ultra-high density polyethylene sucker rod guide having an ultra-high molecular weight in the range of from about 2 million to about six million and characterized by superior resistance to impact, wear, cracking, abrasion and corrosion, a high tensile strength, a relatively high coefficient of thermal expansion and a low coefficient of friction.
A still further object of this invention is to provide a generally cylindrically-shaped, extruded, ultra-high molecular weight and ultra-high density polyethylene sucker rod guide provided with a longitudinal, circumferentially grooved sucker rod bore which is slightly undersized with respect to the sucker rod to which the guide is attached, and a longitudinal, tapered slot extending through the sucker rod guide body and communicating with the sucker rod bore, for mounting the sucker rod guide on the sucker rod.